fix(desktop): restore bulk "Archive all sessions" button + align header actions

[OmarB97]

Why

The fork-built bulk "Archive all sessions" button (commit 5048f11) disappeared from the sidebar. Root cause: the desktop-build-restoration (#127) rebuilt ChatSidebar without the onArchiveAllSessions prop, so the controller wiring, the header button, and the confirm dialog were all dropped — only useSessionActions.archiveAllSessions survived, unreachable. The operator also flagged that the remaining header button wasn't aligned with the "Sessions N/M" count label.

What changed

• desktop-controller.tsx: pass onArchiveAllSessions={() => archiveAllSessions().then(refreshSessions)} again (the surviving action hook, re-wired).
• chat/sidebar/index.tsx: re-add the onArchiveAllSessions prop, archiveAllOpen/archiveAllSubmitting state, handleArchiveAll, the restored ArchiveAllSessionsDialog, and the archive button. The Sessions header action is now one flex items-center gap-0.5 row holding the archive button and the group-by-workspace toggle, each in a fixed size-6 slot. Since the header row is items-center justify-between, both buttons stay vertically centered with the "Sessions" count label, and the fixed slots keep the row height (and the label baseline) stable as buttons show/hide across views — fixing the misalignment.
• i18n: the dialog/button strings are now localized (the sibling group toggle was already i18n'd; the original feature shipped hardcoded English). Added sidebar.archiveAll* keys to en/zh/ja/zh-hant + types.
• Archive icon spins while submitting; button is disabled when the list is loading, empty, or a submit is in flight.

How to review

1. desktop-controller.tsx one-line prop re-wire.
2. The header headerAction block in index.tsx — confirm the two size-6 slots + flex items-center give the alignment, and the group toggle is byte-unchanged from before aside from being nested in the new flex row.
3. ArchiveAllSessionsDialog + the new i18n keys.

Evidence

• Restores behavior from 5048f11 (the original bulk-archive PR); archiveAllSessions in use-session-actions.ts is unchanged and already shipping.

Verification

• apps/desktop: tsc -b 0 errors; vitest src/app/chat src/i18n — 39 passed. Built into the packaged app and swapped onto the running install for visual confirmation of the button + alignment.

Risks / gaps

• Visual alignment is verified in the rebuilt app, not by an automated snapshot (desktop has no visual-regression harness) — low risk, the layout mirrors the original shipped feature.
• No new logic in archiveAllSessions itself — purely restoring the UI entry point and wiring.

Collaborators

• @OmarB97 (operator)
• Claude Fable 5 (Claude Code)

[github-actions]

🔎 Lint report: fix/restore-bulk-archive vs origin/main

ruff

Total: 0 on HEAD, 0 on base (➖ 0)

🆕 New issues: none

✅ Fixed issues: none

Unchanged: 0 pre-existing issues carried over.

ty (type checker)

Total: 10554 on HEAD, 10554 on base (➖ 0)

🆕 New issues: none

✅ Fixed issues: none

Unchanged: 5544 pre-existing issues carried over.

Diagnostics are surfaced as warnings — this check never fails the build.